Who is taking the snap isn’t the question.
The question is, can that person pass the ball well.
Teams are not required to have 2 active QB. They can go with 1 QB if they like. Of course, they risk having zero effective passer if QB1 goes down.
Teams can have 4 active QB if they like. But then they will have 3 active staying on the sidelines, not contributing much.
The scenario with Taysom is the Saints can go with 1 QB Carr and Taysom as TE-X. If Carr goes down, then they’re kinda out of luck.
The requirement for 2 “bona fide” QB is the ability to designate an emergency QB. If that emergency QB comes in, only he can take the snap. Also, that emergency QB can not line up anywhere else; not as RB, TE, special team, punter, etc.
You can go to game day with 3 QB, say QB1 Carr, QB2 Winston, QB3 Hill. Then they can line up where ever. But no emergency QB.
You can go to game day with 2 QB, say QB1 Carr, QB2 Winston, TE-X Hill. Then they can line up where ever. But in this scenarios, they can designate Haener as the emergency QB.
They can go with QB1 Carr, QB2 Hill and designate Winston as emergency QB.
The requirement for bonafide QB is so the team can’t say QB1 Carr QB2 Kamara TE-X Hill and then designate Winston as an emergency QB
Questions left unanswered by the NFL clarification is how often a team can change the player position; Eg can the Saints flip Hill as a QB or TE whenever they want?